Generally, aluminum has a surface on which an oxide film is formed. Since this oxide film has low adhesiveness to solder, aluminum cannot be soldered using ordinary solder for copper. Accordingly, in the case where a base material made of aluminum is soldered, it is necessary to use special flux having high activity that is enough to allow removal of this oxide film, and also necessary to use, as a base material, aluminum having a surface plated with dissimilar metal, as disclosed in Japanese Patent Laying-Open No. 2004-263210 (PTD 1).